The present invention relates to a process of preparing trans-1,4-cyclohexanedimethanol and powder of the same, which is useful as raw material for polyester resin, polyester synthetic fiber, polyester coating material and the like, or as chemical intermediates.
1,4-cyclohexanedimethanol (hereinafter may be referred to as 1,4-CHDM) is industrially prepared by distillation, for example, by hydrogenating 1,4-cyclohexanedicarboxylic acid dimethylester in the presence of copper-chromium catalyst and then distilling the hydrogenated compound.
1,4-CHDM thus prepared comprises usually about 70% by weight of trans-1,4-CHDM and about 30% by weight of cis-1,4-CHDM, and, this product is waxy or mascuite-like at room temperatures.
The melting point of cis-1,4-CHDM of high purity is lower than room temperature, and it is liquid at room temperatures; on the contrary, the melting point of trans-1,4-CHDM of high purity is 60.degree. to 64.degree. C. and it is solid at room temperatures.
Polyester resins made from trans-1,4-CHDM have high glass transition temperatures and high softening points, and they are superior in the properties of the resin. Therefore, trans-1,4-CHDM is preferable as the raw material of polyester products.
Conventional processes of preparing trans-1,4-CHDM are shown below:
(a) a mixture of cis-and trans-1,4-CHDM is converted in trimethylsilyl compound and the compound is separated by diglycerol column chromatography, as disclosed in Acta Pharmaceutica Suecica 5(5), pp 449-456(1968).
(b) A mixture of cis- and trans-1,4-CHDM is separated by cyclodextrine-combined silica gel column chromatography, as disclosed in Journal of Liquid Chromatography 10(6) pp 1077-1084(1987).
(c) A mixture of cis- and trans-1,4-CHDM is converted to dibenzoate compound, and the compound is selectively crystallized by utilizing the difference of crystallization and then hydrolyzed to obtain trans-1,4-CHDM, as disclosed in Journal of the Chemical Society pp 404-407(1953).
However, according to the conventional processes described above, high purity trans-1,4-CHDM may be obtained only in small amounts by the distillation, and the majority of distillate is a mixture of trans- and cis- 1,4-CHDM containing about 30% of cis-1,4-CHDM, the mixture having a melting point of about 40.degree. C.
1,4-CHDM containing about 30% of cis-1,4-CHDM has the disadvantages described below.
For example, in the case of commercial transportation, expensive drums are needed, because the compound is waxy or mascuite-like. This compound requires previous heating at temperatures of 50.degree.-60.degree. C. prior to its use, and it is decomposed or colored by heating or melting, therefore its use is restricted. Heating or melting is expensive and therefore, the product made from it becomes more costly to produce. Thus, there are a lot of disadvantages.
Further, the conventional processes of preparing trans-1,4-CHDM as shown in examples (a)-(c) above are analytical processes or laboratory processes. These processes suffer from many disadvantages, such as: low yield, high production costs, and complicated manufacturing processes. Therefore, the conventional processes are not fit for commercial production, and they are not satisfactory for producing trans-1,4-CHDM or powders thereof.